Reversible screw thread cutting device



June 14, 1960 J. BERNHARD REVERSIBLE 'scREw THREAD CUTTING DEVICE 3 Sheets-Sheet 1 Filed March 14, 1956 June 14, 1960 J. BERNHARD REVERSIBLE SCREW THREAD CUTTING DEVICE Filed March 14, 1956 3 Sheets-Sheet 2 June 14, 1960. 1. BERNHARD REVERSIBLE SCREW THREAD CUTTING DEVICE 5 Sheets-Sheet 3 Filed March 14. 1956 United States Patent REVERSIBLE SCREW THREAD CUTTING DEVICE Johann Bernhard, Nacka, Sweden, assignor to Aktieholaget Svenska Precisionsverktyg, Nacka, Sweden, a corporation of Sweden Filed Mar. 14, 1956, Ser. No. 571,519 Claims priority, application Sweden Mar. 18, 1955 11 Claims. (Cl. 192-56) This invention relates to reversible screw thread cutting devices.

More particularly'this invention relates to a coupling between a driving and a driven member of a reversible screw thread cutting device, said coupling comprising two surfaces rotatable relative to one another and extending in planes transverse to the longitudinal laxis of the device and provided with at least one coupling element adapted -to enter recesses in one surface, said coupling element and said recesses being axially displaceable relatively to one another and adapted at a predetermined value of the torque to take a position where lthey are disengaged from one another.

Still more particularly this invention relates to a coupling between a driving and a driven member of a reversible thread cutting device of the type particularly adapted for thread cutting of bottom holes.

One main object of the invention is to provide a coupling adapted to cause the torque acting upon the screw tap secured to the driven member totally to cease actuation of said driven member, when the resistance to the turning movement of the tap reaches a predetermined value.

To overcome the difficulties inherent in this problem, several coupling constructions automatically reacting on overload have been proposed heretofore without, however, entirely attaining the desired result, since the force required to disengage the elements of the coupling would continue to act upon the screw tap. Further, if the coupling is of the snap-in type, the screw tap may be stuck fast in the thread and the coupling may overheat because of the friction.

A further object of the invention is to provide a coupling adapted in a more reliable manner than the constructions hitherto known to eliminate the various dithculties mentioned hereinbefore.

Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawingswhich form part of this specification and of which:

Fig. 1 is an axial sectional view of a screw thread cutting device provided with a coupling constructed according to one embodiment of the invention.

Fig. 2 is a partial axial section taken perpendicularly to the section shown in Fig. 1.

Fig. 3 is a plan view of an intermediate annular member forming part of the coupling.

Fig. 4 is a partial axial section of a coupling constructed according to a modified embodiment of the invention.

Fig. 5 is a plan view of two annular members comprising in this modified coupling in engaged position.

Fig. 6 -is a further plan View of the annular members shown in Fig. 5 in disengaged position.

Fig. 7 is a perspective view of these same two annular members, in the engaged position shown in Fig. 5, and also showing a driving spindle comprised in the device.

Fig. 8 s an axial sectional view of a screw thread cutting device having a coupling constructed according to embodiment illustrated in the Figures 1 to 3.

LCC

still another embodiment of the invention, the centr'al carrier being removed.

Fig. 9 is a partial axial section taken at right angles to the view of Fig. 8. Y

Fig. 10 is a plan view of an annular member forming part of the coupling shown in Figures 8 and 9.

Fig. 11 is a View in elevation of a part of the coupling shown in Fig. 8, the protecting cap of the device having been removed :to illustrate positions relative one another of the couplingmembers of the device.

Referring to the drawings, the reference numeral 10 designates the driving spindle of a driving member forming part of a screw thread cutting device, said spindle having its one end widened to form a sleeve shaped portion 12, on the external side of which is secured a pro.

tecting sleeve 14 which also partly surrounds a further sleeve 16. Said sleeve 16 is screwed onto a guide body 1S that is mounted in the driving member and that projects axially within a space 20 formed by the portion 12 andthe sleeves 14, 16. Itis held in said portion by means of balls 22 that run in opposed annular grooves 24, 26 provided in the guide body 18 and the portion 12, respectively. The balls 22 may be introduced through a radial `bore 28 that is thereafter closed by means of a plug-.30. Concentrically within `the guide body 18 is mounted a further sleeve member 32 carrying on its one end 'aholder 34 for a screw tap not shown in the drawing. The holder 34 is driven by a pin 36 on rotation of the sleeve 32. The sleeve member 32 with the holder 34 is suspended and `balanced by a spring 38 secured at onev end on a pin 4t) disposed in a cap member 41 that engages in a recess in sleeve 32 and secured at its other end to a pin 42 carried by an end cap 44 of the member 32 that seats in a recess in the bore of guide body 18. A second spring 46, more powerful but shorter than the spring 38, is inserted between the end cap 44 and an abutment 48 of ythe member 32. Said spring 46 has for its object to impart a certain resiliency to the member 32, when the screw tap is set against the workpiece.

The bearing between the guide body 18 and the inner sleeve member 32 is provided by a great number of small yballs S) inserted between the cylindrical surfaces of said guide body and said sleeve member. The balls are kept in their position by a ball holder 52, which also fixes the position of `a single ball 54 having a diameter considerably larger than that of the balls Sil. The ball 54 transmits the torque between the guide body 1S and the sleeve member 32 due to its entering axial grooves 56 and -58 provided in said body and said sleeve member 32, respectively. For the particulars of the construction and operation of the torque transmitting ball reference is made to the specification of the Patent 2,592,10310 U. A. Alfreden.

To transmit the rotary movement of the driving meniber substantially constituted by the spindle 10 with`its sleeve shaped portion 12, to the driven member broadly comprising the guide body 1S and the inner sleeve 32 with its holder 34, there is provided a coupling between said members. Said coupling may have the construction shown in Figures 1 to 3 and include an annular member 6l) interposed between two annular surfaces extending in planes perpendicular -to the axis of rotation of the screw thread cutting device. The upper of said annular surfaces, which is denoted by `62, is formed on the lower edge of the widened portion 12 of the driving spindle 10, the other, which is denoted by `64, being formed on an annular ange 66 that projects, from the guide body 18. Provided in the interposed annular member `60 is a number of axially Vextending through-bores '58; circumferentially evenly distributed in two diametricl ly opposed groups, each comprising three bores in the Between This intermittently effected coupling of the driving and" driven members of the device provides a particular advantage during the reverse movement, particularly if the screw thread cutting operation is performed in a relatively soft material which has a tendency to lock the screw tap.

The embodiment of the coupling shown in Fig. 8 likewise comprises a spindle 10 having a widened portion 12 and, the protecting sleeve 14, the sleeve 16 and the guide body 18 located in the space 20. The sleeve shaped portion 12 is rotatable as in the preceding embodiments, but in the axial direction it is rigidly connected to the guide sleeve 18 by means of the balls 22 running in the opposed roller ways 24, 26. In the same manner as is shown in Fig. 7 representing the preceding embodiment, the portion 12 of the spindle 10 is formed with three peripherally evenly spaced shoulders 106 leaving interspaces 108 therebetween. The transitions or faces between the interspaces and the shoulders are preferably located in axial planes. The coupling between the driving member and the driven member, i.e. primarily the guide body 18, is substantially constituted by two annular members 110, 112 disposed concentrically relative to one another and located adjacent the sleeve shaped portion 12, and by a further annular member 114 underneath the annular member 110. The inner member 112 of the first-mentioned pair of annular members is rotatably but axially stationarily mounted on the guide body 18 by a plurality of balls 113 inserted into two annular roller ways 116, 118 facing one another and provided in the ring 112 and the guide bdy 18, respectively. The rotary movement of the member 112 relative the spindle 10 is limited by means of circumferentially evenly spaced pins 120, the number of which is three in the illustrated embodiment, and which in the axial direction are rigidly secured in the portion 12 and have projecting end portions engaged in recesses 122 provided in evenly spaced relation about the circumference of the annular member 112. Evenly spaced shoulders 124 are formed in the lower circumferential edge of the member 112, the device illustrated in the Figures 8 to l0 having three such shoulders intended to engage correspondingly formed and spaced shoulders 126 on the adjacent circumferential edge of the annular member 114. The concentric pair of annular members 110, 112 are held rotationally stationary relative to one another by having their opposed surfaces formed with semicylndncal, axially extending grooves 128, 130 housing balls 132. These grooves are uniformly spaced about the axis of the coupling. The embodiment illustrated has three pairs of grooves, each pair being formed in the opposed end side walls of the three annular members and extending almost to the opposite end edge surfaces of the members 110 and 112, respectively so as to cause the remaining portions of the members to hold the balls 132 locked in the channels thus formed by the pairs of grooves. A similar system of channels, forming grooves 133 with uniform circumferential spacing between the first-mentioned grooves is formed in the annular members 110 and 112 to house axially extending helical springs 134. These springs 134 permit an axial spring-loaded displacement of the annular members 110 and 112 relative one another. The upper end edge of the `annular member 110 has shallow recesses 136, which may be V-shaped grooves, as is shown in Fig. 1"l. Said recesses house balls 138, that project above the groove edge to co-operate with the recesses or spaces 108 and shoulders 106 of the driving member 12. On both sides of the recesses 136 the upper end edge surface of the annular member 110 is formed with surface portions 111 sloping toward the recesses at an angle of a few degrees relative to a radial plane. The surface portions 111 constitute roller ways for the balls 138, as will be described more in detail hereinafter. Said portions 111 merge with steps 123 extending in otherradial planes, leading to the end edge surface of the annular member 110. The lower end edge of the member is plane, and is thus adapted to slide on the shoulders 126 of the annular member 114. Said member 114 is rotationally stationary but axially displaceable relative to the guide body 18 due to a ball 140 housed in a channel formed by the axial grooves 142 provided in opposed surfaces of said annular mem` ber 114 and said guide body 18. Axial displacement of the member 114 is eiected against the action of a plurality of axially extending helical springs 144 that are uniformly distributed circumferentially about the lower edge of the member. The preferred number of springs is twelve in the embodiment illustrated, and they are inserted in semi-cylindrical recesses 146 extending in the axial direction and provided about the external face of the guide body 18 and the internal face of the outer sleeve 16. The lower ends of the springs 144 rest on an annular member 148 that is rotatably mounted on a shoulder 149 formed in the interior of the sleeve 16. Said annular member is kept in contact with said shoulder by means of a washer 150, that is engaged in an annular groove 151 provided in the inner wall of the sleeve 16.l The member 148 has semicircular projections along its interior periphery, said projections being distributed in the same manner as lthe recesses 146 that house the springs 144. Further, the member 148 has four depressions 157 diametrically opposed in pairs andv extending from the lower surface of the member. Each depression houses a ball 152 pressed against the member 148 by the action of a helical spring 153. Said springs 153 are located in axial bores provided in the lower portion of the sleeve 16. For the purpose of varying the tension of the springs 144 and consequently the pressure of said springs against the annular member 114, the sleeve 16 is threaded onto the guide body 18, as is indicated at 160.

A locking device is provided to prevent jamming between the lower end of the sleeve 16 and a stop shoulder 158 formed on the guide body 18, said locking device being formed so as to become operative before said sleeve comes into contact with the shoulder when the sleeve is screwed down on the body.V In the illustrated embodiment the locking device comprises an axial shoulder. 155 projecting from the end of the sleeve, and a radial pin 156 rigidly secured to the guide body 18. As will be readily understood, a peripherally directed locking force is thus created, which prevents jamming during any axial displacement of the sleeve 16 and the guide body 18 relative to one another.

When a thread cutting operation is to be' commenced, the various elements of the thread cutting device described hereinbefore take the positions illustrated in the Figures 8 and 9. The power transmission from the driving spindle 10 is effected through the shoulders 106, which are in engagement with the balls 138, to the outer annular member 110, and thence through the balls 132 to the inner coupling annular member 112, which in turn transmits the torque through its shoulders 124 to the annular member 114, by engaging the shoulders 126 of said member. The power is then transmitted to vthe guide body 18 and from the latter to the members (not shown) in the Figures 8 to l1 carrying the screw tap chuck. When in the operation of boring a bottom hole the screw tap reaches the bottom of the hole and, the torque increases momentarily between the driving and driven members. The balls 138 of the outer annular member 110 will then leave the grooves 136 andjroll up onto the sloping portions 111 of said member, asis illustrated in Fig. 11. y

When the balls 138 have passed over a predetermned portion of said sloping tracks 111, the axial displacement of the annular member 110 will have proceeded so far as to bring the lower uninterrupted end edgesurface of said member to a level with the lower surfaces f'f'the Ylower :annular member 114, "resulting in inter- -ruptionof Vthetorque 'acting-on the member 18 that carries the screw tap.4 "However, since sliding Vfriction f still existsbetween'theV uninterrupted planelower end sur- "faceo'f the 'annularmember 110 and theshoulders "126 'of ther-annular member V114, the'balis'138 arevcaused to continue their upward rolling movementYonthe sloping "portions I-Ilto anfend position'on the stepsY 123,--which iposition is `determinedfbythe :pins 1120 encountering one end offthe'rercesses` or grooves-122 provided in the-inner "As is readily understood, this Ihe oper-ation describedensures a uniform and vibrationless disengagement of the coupling alongan uninterrupted path "atthewery'moment Awhenlthe screw tap' reaches the bottompf the hole subjected to thethread cutting oper'- -Yation. .Y When the screwrtap isr'rtofbe removed fromthe ,-hole, the 'spindle 10-is caused to rotateinthe opposite fdirection, theballs v`138 of'the outer annularfmember 114i then roll backlinto ther-grooves 136, asis readily understood. Asa consequence, theV annular member 1110 is moved-upwardly by theaction of the'springs 134. This movement causes the'isho'ulders 126 ofthelower Aannular vmember-114 again to engagethe'shoulders "124 of the inner annular member 112. Y The member 114 is thus causedlto rotate, and its rotary move'mentfis transmitted Vthrough-the ball 14B to the'guide body Y18,'andfrom said u body t0 the screw-tap.

'-While severalmore or less -specicrembodiments ofthe invention have been shown and described,itis to be understoodthat this is for purpose 'of illustration only,

andthatthe invention Visrnot to be limitedthereby,but

its-'scope is to be determined by the appendedclaims. Y

" V'Whatl 'claim is: Y

'-'1.;Acoupling;fori a screw thread cuttingr'device orthe likefcomprising arotary vdriving member, a "rotary-"driven member, #and clutch means `to connect said members to )transmit 2a torque Vand to' disconnect 'said members -when "'saiditorque exceeds .alpredetermined value, :said Vclutch means vincluding 'threeelements one of said elements beingzadapted tobe driven by said'driving'member and fhavinga toothedsurface,y a second of said elements being mounted coaxially with said first element in axiallyspaced-relation thereto'and 'being formed 'with a toothed f surface 'opposed 'to -the yErst-named toothed surface -and -adaptedto'cooperate'therewith, said two elements being 'movablehaxiallyrrelative toleachother, said toothed suri'faces 1beingmounted toengage to transmit torque, 'and said' third element `being mounted coaxiallyv of .one of said Yother twoelementsfarld lbeing Yformed withaa smooth annular-surface, Ysaid-third element ,being mounted to move axially Sat and above a predetermined torque to Vfonceitssmooth annular [surface to engage one of said V`to'othedfsurfaces to move one of said Yrst two elements 4 axially-to disengage saidY cooperating toothed surfaces and t rto'holdsaid toothed surfaces out of engagement, and said third element being springapressed to disengage said one toothed surfacebelow--said predetermined torque to permit l-'saidftoothed surfaces to engage to transmit -said torque.

Y523A coupling tor-a screw thread'cutting device vor the "like comprisingfa rotarydriving member, a rotary driven f member, and clutch means topconnect said members toVV ftransmit-a-torque and to disconnect said members whenv 'saidtorque exceeds a predetermined value, said clutch :means including -three cooperating coaxially mounted Y g8 of 'said elements fbeing 'mounted J to movefaxiatly rofsaid driven member andto 'rotatezwithfsad cdrivenz'member, saidfrst :and jsecond elements having- .cooperating Y:faces spring-pressed into @engagementvand iformed rkwith projections and recesses to engage .to transnlittorque-from said driving member to said driven member, vsaid third v-elementtbeing mounted to be drivenby'saidsdrivingmember and `for-'.ax-ial movementlrelative to vsaid AViii-stand second elements, said .third element having a-ismooth 4annular surface mounted tofengage' at least a'portion of saidface of said second element, said driving member havinga face Sformed with. a plurality- @f axially-projectng shoulders, .said third element having a `rradial nface imountedttoconfront theiradial face OsaiddriVingmem- Vber andformed with a 'plurality ofrrecesses that-have Y sides inclinedtothe axis .of said element, alpluralityof balls interposed .betweenfsaid radialfaces and corresponding innumber tosaidrecesses, andspringrineans,mounted constantly to urgey :said vthird element .axially to .urge Vsaid radial .faces toward=one another'and to seat said balls in said recesses .below a predetermined lvalue Y'of torque, and to Vpermit saidshoulders to engage 'said balls toimove them out .of -theirrespective vrecesses to shift said thirdrelement axiallyvrelativeto said driving member at andlabove a predetermined value 'of torque to engage the smooth annular surface of saidthird elementy against the face of said second elementtoshiftsaid secondelement axially to Ydisengage said. cooperating faces to permit said driving member tofrotate ireelyfrelativeY to `said driven member andlto'permit saidrsmooth annularfsurface of said third ,elementtoislide on"the1face`of`-said second element.

3. A coupling for a screwthreadcuttingfdevice-br the like comprising a rotarycdrivingv member, -a rotary drivenA member coaxial theewith,and `clutch means to connect said Lmembersvto transmit torque and Ltojdisconnect said-members when said-torque exceeds a predetermined value, said clutchV means including three rings mounted coaxial with saidrmembers,"means for connecting said first ring 'to i said driving fmember to drive said iirst ring'from said drivingmember,fsaid first .ring being provided with .projections equi-angularly Y spaced about theicommon vaxisaof said'members, a secelements, agiirs'tV of -said elements being *mounted'to tbe driven -byf said drivingy member, a second ond ring mounted to rotate with vsaid driven-member in Yaxially-,spaced andV axiallyfmovable relation tosaid .first ring, said vsecond ringbeing formed Switha plurality of portions equifangularlyspaced about said common axis and'adapted-to engage the'projections `ofsaid iirst ring, spring means'constantlymrging :said second ring y,axially to place said portionsrin engagement with said projections, said third .ring beingmounted coaxially of said iirst ring and for limited axial movement relative to Vsaid members and said Viirst andfsecond rings, said third Yring havingapluralityxofsequiaangularly spaced v,recesses in its ,upper face, said recesses having thesides .thereof inclined lto'said commorliaxis;saiddriying member having its lower face disposed to vconfr-ontthe upper facelof said third ring and formed with'equi-angularly spaced projections corresponding in number. to said recesses, -a Y.plurality of balls interposed between said con- Vfronting faces and vadapted to seatv in said recessesv to lbe engaged by said last-namedprojections .to Arotate said third ring upon rotation'of said drivin-g member, and spring means mounted constantly to urgeA said thirdfring axiallyagainst said balls to seat saichballsinr'saidrecesses below said .predetermined -value of torque, said third ring being formed with AaY smooth annular-.lower face disposed at a right angle ,to said commongaxis, the said portions of said second ring'having'plane upper facesv confronting'said annular lower lfa'ce of said third ring, the tiret-named spring meansbei'ng adjusted to perlmit the last-namedprojections tounseat said' balls 'from theirv respective recesses Vat'and above a `predetermined valueV of'torque to'move saidthird' ring axially to engage the smooth jvlower -VVface thereof *against the plane t 1:1 ingr-Perte as mtas-y drivenpart, {mrt-V rneasaxralrgdi in Series` @Wem Seid- Parts; cegepsngzplraiy 'Qfwfqueztransf mining, `reletiyely ax'gly Y111Qv-alae annularmmbrs op@ of said annular members and one of said parts hayi-ng confronting faces,A oneV orf-s aigl faceshjavxzggi k'shoulders hfreenfheohes faQQ-havingsresessss therein. and having incline@ Port-ionsadoningsad; recesses balls inter: posedrbetween sa-idjfaces vand@cooperating with seiclvshoulders andrecesses to effect transmission of-torqnebetween said one part and said one annulanmember, separate coupling means` disengagegblysconnecting twoA of said annuler members, springs. constantly urging said balls and .said coupling; means Ytoward engaged torique-trans-l rnittijag.v pstin, one 0f Said annular members-having a smooth surface extending for a,- dstance aroundits axis,

tween. Sai@ parts; for@ transmitting; remue be: l

saidv balls,y beingadapted when@ predetermined -value Y of Y torquefis exceeecl-A to Inlove out-,of torque-transmttingposition andl to roll onV said inclinedport-ions and onto said smooth surface thereby to move said coupling means out Givperetive. @slice Seidpbells when; engaged withY ,Said smooth ce. bef g;A operative toV keg-p `4 seid A coupling meansposrt'lvelyl in; @operative position and:Y allowrotatQnOf .said zdliyins, part without transmission; Gf torque toslid,drh/61.1;paraY References Cited in the le of'this patent UNITED' STATESv PATENTSv 

